It is a canadian sex act where milking girl is on all fours, with her breasts hanging in free air, then they are milked like a cow, with occasionally giving her nipple crunch, and some light punches in the breasts. To make it more interesting usually a man also does the girl in her ass in doggie style during this.

When she said she had delivered baby just a few months ago, the gang got excited to do Manitoba milk bag with her